This Fifth Annual Report summarizes work performed by the Smithsonian Astrophysical Observatory (SAO) for NASA Goddard Space Flight Center (GSFC) under Cooperative Agreement NCC5-368. The Agreement is entitled 'Constellation X-ray Mission Study and Support.' This report covers the period from October 1, 2002 through September 30,2003. The report summarizes the main areas of SAO activity. Most of the work has been done jointly with personnel from GSFC and Marshall Space Flight Center (MSFC). We describe SAO participation in these efforts. In spite of the work being mainly a level of effort, a significant amount of work was accomplished. Under the Agreement, SAO performed work in eight major areas of activity. These areas related to: 1) Constellation X-ray Mission Facility Definition Team and Study Management; 2) Science Support; 3) Spectroscopy X-ray Telescope (SXT); 4) Systems Engineering; 5) Travel in Support of the Work Effort; 6) In-house Management and Coordination; 7) Technical Readiness and Implementation Plan (TRIP) Report and Follow-up; 8) Industry Liaison and Study Preparation.